Swimming pool cover

ABSTRACT

Apparatus for covering a swimming pool when not in use comprising a bridge adapted to be positioned adjacent to the pool and movable from a lowered position of use to a raised position sufficiently elevated to allow normal use of the pool. The cover is carried in stored condition on the bridge. The cover is extendible to cover the pool in the lowered position of the bridge.

l Unite States Patent 1111 Myles Dec. 11, 1973 SWIMMING POOL COVER 3,002,195 10/1961 Prudek 4/17211 3,051,964 91962 P h t l.. [75] Inventor: J. Edgar Myles, Fraser, M1ch. 3209373 1011965 i za i [73] Assignee: J. E. Myles, Inc., Detroit, Mi h, 3, 13,661 12/1968 Ross 4/l72.13

[22] Filed: 1972 Primary ExaminerHenry K. Artis [21] 237 431 AttorneyCharles R. Rutherford et al.

521 U.S. c1. 4/172.14 [57] 51 lnt.Cl E04h 3/16, E04h 3/18 Apparatus for Covering a swlmmmg P when not In [58] Field 61 Search 4/172, 172.11, 172.12, use comprising a bridge adapted to be positioned j 4l17213, 172 14 cent to the pool and movable from a lowered position of use to a raised position sufficiently elevated to 5 References Cited allow normal use of the pool. The cover is carried in UNITED STATES PATENTS stored condition on the bridge. The cover is extendible to cover the pool in the lowered position of the 3,009,166 11/1961 Sears 4 172.11 bridge 3,264,656 8/1966 Clay et a1 4/172.l2 I 3,564,622 2/1971 Meulekamp 4/172.l3 14 Claims, 11 Drawing Figures MIENIEnuEc 11 1915, 3777.319

. sum 10? 4 PIC-3.2

l SWIMMING POOL COVER BACKGROUND AND SUMMARY OF THE INVENTION Extendible and retractable swimming pool covers have been used in the past. Examples of such covers are shown in the following patents:

McGuire Re 25,078 Nov. l4, I961;

Lamb 3,050,743 Aug. 28, I962;

Logan 3,063,062 Nov. 13, I962;

Bartolucci et al. 3,l48,384 Sept. 15, I964;

Myrtha 3,541,615 Nov. 24, 1970;

Peterson et al. 3,566,420 Mar. 2, I971.

The present invention constitutes an improvement over the prior art bythe provision of a beam assembly preferably in the form of a bridge which can be raised and lowered and which carries a flexible pool cover. When the beam assembly is in the lowered position, the pool cover may be extended and secured around the edge of the pool. When not in usethe cover may be rolled up and stored on the beam assembly and the beam assembly elevated sufficiently to allow normal use of the pool.

As an additional feature of the invention, hydraulic piston-cylinder means are provided for raising and lowering the beam assembly.

Additional objects and features include a novel hydraulic system, an improved beam assembly, and guide means for supporting the piston-cylinder means in a telescoped condition capable of retracting and extending to raise and lower the beam assembly.

Further objects of the invention include the mounting of the beam assembly either adjacent one end of the pool in which event only one cover sheet is required, or intermediate the ends of the pool in bridging relation thereto in which case two cover sheets may be employed.

Other objects and features of the'invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a perspective view of apparatus embodying my invention, showing the beam assembly. in raised position intermediate the endsof the pool.

FIG. 2 is similar to FIG. 1, but shows the beam assembly in its lowered position of use.

FIG. 3 is a perspective view of a modification in which the beam assembly is located adjacent one end of the pool.

FIG. 4 is an elevational view with parts broken away and in section showing the mounting in the ground of one of the piston-cylinder assemblies for raising and lowering the beam assembly.

FIG. 5 is a top plan view of the beam assembly with parts broken away.

FIG. 6 is a detailed view of one of the rollers upon which a cover sheet is adapted to be stored.

FIG. 7 is a diagrammatic view of the hydraulic system for raising and lowering the beam assembly.

FIG. 8 is a fragmentary elevational view with parts in section showing a modification in which the bridge is mounted wholly above ground. 1

FIG. 9 is a fragmentary view with parts in section showing a portion of FIG. 8 on an enlarged scale.

FIG. 10 is a plan view of an improved fastener device for securing the cover around the edge of the pool.

FIG. 11 is a vertical sectional view of the device of FIG. 10 showing the fastener member retracted in solid lines and elevated for use in dotted lines.

Referring now more particularly to the drawings and especially to FIGS. 1 and 2 thereof, the beam assembly is shown as a bridge generally designated 10 which straddles a pool 12 intermediate its ends. The pool is shown as rectangularbut may be of irregular or other shapes as may be desired. The bridge is shown in FIG. 1 in its raised position elevated sufficiently to permit normal use of the pool and in FIG. 2 in its lowered position when it is desired to cover the pool.

The bridge comprises a pair of columns in the form of vertical supporting units or piston-cylinder assemblies 32, hereinafter described, and an elongated horiiontal beam 13 having a bar 14 extending transversely across the width of the pool and also having the mounting plages 16 secured to its ends.

Rollers 18 are carried by the plates 16 upon which the pool cover sheets 20 are adapted to be rolled up and stored. Each roller 18 comprises a roller tube 22 having spindles 24 secured to the ends which are journaled for rotation in the plates 16. The pool cover sheets 20 are rolled up on the roller'tubes 22 for storage when not in use. These cover sheets may be of any suitable material for the purpose which is flexible and preferably does not absorb or transmit water. A waterproof canvas material might be suitable for the purpose although as stated any suitable flexible material may be used.

The cover sheets 20 are preferably of a shape corresponding to that of the pool and may be secured to the roller tubes 20 as by having one end thereof clamped to the outer surface of the tube by a clamping bar 26. The clampingbar 26 preferably extends for the full length of the tube 22 and is secured to the tube by suitable means such as the fasteners 28. The rollers 28 have cranks 30 secured to the ends of the spindles 24 to enable rolling up the cover sheets.

The bridge includes vertical piston-cylinder assemblies 32 at the ends of the bar 14 of beam 13 for raising and lowering the latter. Each piston-cylinder assembly comprises a cylinder 34 and piston 36 reciprocable therewithin. Each cylinder 34 has a cap 38 secured to its upper end which is rigidly connected to the bar of beam 13. Each piston 36 has a piston rod 40 which extends downward through the lower end of the Cylinder and has its lower end fixed in a socket member 42 at the upper end of a vertical tube 44. As noted in FIG. 4, each tube 44 is anchored on a base plate 46 in a cored out hole in the ground located a substantial distance, for example eight or ten feet, below ground level G. This cored out hole is a vertical cylindrical hole designated 47 and preferably lined with a tube 48 of metal or the like. This tube 48 provides a vertical housing for each piston-cylinder assembly which telescopes therein and which when retracted and lowered is substantially fully received therein. On the other hand, when raised to their elevated positions the piston-cylinder assemblies are extended for several feet above the ground so as to raise the beam 13 to the FIG. 1 position, perhaps eight or ten feet above the ground so that the pool can be used normally without interference.

Each piston-cylinder assembly 32 is at least partially shrouded in a tube 50 the upper end of which is secured to the cap 38. This tube 50 extends downward and telescopes within the fixed tube 48. FIG. 4 shows the bridge extended or raised and it will be noted that even in this position the tube 50 telescopes within the upper portion of the tube 48. The tube 50 will guide the descent of the bridge as it is lowered through its telescoping relation inside the tube 48. A collar 52 fixed on the tube 50 serves as a stop determining the lower limit of the bridge by contact with the upper end of tube 48. The upper limit of the bridge is reached when the piston 36 of piston-cylinder assemblies 32 bottom out.

Each cover sheet preferably is of a shape corresponding to that of the pool and has fasteners 54 around three sides, that is along its side edges and along its free end edge, cooperable with coacting fastener elements 56 provided around the edge 57 of the pool. The elements 54 and 56 may be snap fasteners for example, or the elements 54 may be button-holes and the elements 56 buttons. Any suitable coacting set of fastener elements may be provided by which the margin of each cover sheet may be releasably secured around the edge of the pool.

FIG. 2 shows the bridge lowered and one of the cover sheets 20 extended and fastened around the edge of one-half of the pool. The bridge at this time is in its lowermost position. The other cover sheet 20 may be extended from its supporting roll and fastened marginally to the pool in the same manner. It may be extended merely by pulling its free edge or if desired by rotating the crank 30.

When it is desired to use the pool, the cover sheets are unfastened from the pool margin and are rolled up on the rollers 18 by means of the cranks 30. Then the bridge is elevated by the piston-cylinder assemblies 32 to the raised position of FIG. 1. In the raised position, the bridge is elevated enough so that it will not interfere with the normal use of the pool.

FIG. 3 shows the bridge supported in the ground at one end of the pool. In this instance only one roller 18 and cover sheet 20' is required. The cover sheet 20' must however be of considerably greater length in order to cover the entire area of the pool. Otherwise the cover sheet 20' is like cover sheets 20.

FIG. 7 illustrates the hydraulic system for raising and Valve 68 normally assumes the position illustrated in which the lines 65, 76 and 78 are drained to tank 90. The line 72 at this time also is connected to tank. Energization of solenoid 92 moves the valve 68 to position 1, and energization of solenoid 94 moves the valve to position 2. When neither solenoid is energized the valve assumes the neutral position illustrated.

A pressure regulating valve is diagrammatically shown at 96. This valve, when the pressure in line 72 is below the limit of pressure of the valve, will be closed to block communication of line 72 to tank through the drain line 98. The pressure in line 72 is applied to the valve 96 through line 100 and when such pressure reaches the set pressure of the valve, the valve is operated against the pressure of spring 102 to align its passage 104 with the drain 98 and relieve the excess prssure A suitable pressure switch 104 is provided in line 72. When the pressure in the line 72 reaches a predetermined value, this switch operates to automatically turn off the motor M. This switch is employed to stop the motor and hence the pump 70 when the piston-cylinder assembly bottoms out in a direction to fully raise the bridge. At such time, the increase in pressure in line 72 is sufficient to operate switch 104 and turn off motor M. Switch 104 may, for example, be set to operate at 50 p.s.i. and the pressure limiting valve 96 at 60 p.s.i. The normal pressure in line 72 to raise and lower the bridge is less than 50 p.s.i. except of course at the upper limit of the bridge when the pressure will increase sufficiently to operate switch 104. The bottoming out of pistons 36 normally occurs, operating switch 104 to shut off motor M, before timer T times out.

In use, when it is desired to raise the bridge, the solenoid 94 is energized to shift the valve 68 to position I which connects the line 72 from pump 70 to line 65. At

. this time, lines 76 and 78 are connected to tank 90.

lowering the bridge. As there shown; the lower ends of the cylinders 34 are vented at 60. The upper ends ofthe cylinders are connected by hydraulic lines 62-and 64 which merge into the common line 65. There is a check valve 66 in each of the lines 62,64 permitting flow in a direction toward the cylinders 34 but normally preventing reverse flow. A solenoid controlled valve 68 is provided to connect the line 65 with the pump 70 by way of hydraulc line 72. A manual on-off valve 74 may if desired be provided in line 72. The pump 70 is operated by a motor M which has a suitable button (not shown) for starting it. A timer T on the motor automatically turns it off after it has been running a certain length of time.

Hydraulic lines 76 and 78 lead from valve 68 to the check valves. These lines are provided to admit hydraulic fluid under pressure to the check valves to open them and allow hydraulic fluid trapped in cylinders 34 to drain out, lowering the bridge. As seen in FIG. 7, lines 76 and 78 admit pressure fluid to the balls of the check valves at the side thereof opposite the side communicating with cylinders 34 so that the balls may be unseated by pressure in lines 76 and 78. Depending on the position of valve 68, lines 76 and 78 may be connected to the pump 70 or the tank 90.

Then by operation ofa manual button or control on the motor M, the motor M is started to drive the pump and deliver hydraulic fluid under pressure into line 65 and into lines 62,64 across check valves 66 to the cylinders 34 above the pistons. The bridge will thereupon be raised to its upper limit. When the piston-cylinder assemblies 32 bottom out there will be an increase in pressure in line 72 sufficient to operate switch 104 and shut off motor M. Check valves 66 will retain the fluid under pressure in the cylinders 34 to hold the bridge elevated.

When it is desired to lower the bridge, the solenoid 92 is operated to shift the valve 68 to position 1 placing lines 76 and 78 in communication with line 72 and placing line 65 in communication with tank 90. Then when motor M is started to operate pump 70, hydraulic fluid under pressure is admitted to lines 76 and 78 to unseat or open check valves 66 and permit the hydraulic fluid in cylinders 34 to be forced back to tank by the weight of the bridge. The motor M will continue to operate until the timer T on the motor turns it off. The operating fluid in lines 76 and 78 is cycled through valves 66 and returned to tank through line 65.

FIGS. 8 and 9 show a modification of the bridge in which it is mounted wholly above ground rather than partly in the ground as in the first embodiment.

In FIG. 8, the bridge is generally designated 10 and has an elongated horizontal beam 13' provided with a bar 14' and one of two rollers similar to those described in connection with the first embodiment on which the pool cover sheets are adapted to be stored. The ends of the beam 13', including its bar 14' and rollers, are carried by mounting plates 16'.

The bridge is generally like that previously described except for being mounted above ground. It includes a pair of vertical piston-cylinder assemblies 32. While only one piston-cylinder assembly is shown in FIG. 8, it will be understood that a pair of such assemblies are provided in spaced relation to one another straddling the pool either intermediate the ends-thereof or adjacent one end, with the beam 13 extending therebetween to form a bridge.

Each piston-cylinder assembly 32'- comprises a vertical cylinder 34 in which a piston (not shown) is reciprocable, having a piston rod extending downward through the lower end of the cylinder with its bottom end fixed in a socket member 42' at the upper end of a vertical tube 44. The tube 44 is anchored on a base plate 46' secured to a foundation surface 45 on the ground surrounding the pool. The plate 46' is anchored to the surrounding foundation surface 45 by anchor bolts 47 and nuts 49.

Extending vertically upward from the base plate 46 is a tubular guide 48' which surrounds and encloses the piston rod 40' and on which is telescoped a vertically slidable tube 50. The tube 50' is .secured at its upper end to a cap or cover plate 38' carried by the upper end of the cylinder 34. The mounting plates 16", on which the ends of beam 13 are mounted, are secured to the lower ends of tubes 50'.

The bridge assembly of FIG. 8 may be moved vertically to an upper position illustrated in the drawing in which the piston-cylinder assemblies 32 are extended. In such position, the beam 13 carrying the rollers for the pool covers is elevated sufficiently so that the pool may be used without obstruction. When the pistoncylinder assemblies are collapsed or telescoped to the lower position, The beam 13' will assume the lower position adjacent to ground level which is adjacent to the top of the edge of the pool so that the pool cover or covers may be extended from their rollers and secured around the edge of the pool when the pool is not in use. As seen in FIG. 9, the mounting plate 16 contact the base plates 46 in the lowered position of thebridge to limit downward movement.

It will be understood that the same hydraulic system disclosed in FIG. 7 for the operation of the first described bridge assembly may be used to operate the bridge assembly shown in FIG. 8. It is emphasized that the principal difference between the bridge assembly of FIG. 8 and that first described is that the assembly of FIG. 8 is mounted entirely above ground. 7

FIGS. 10 and 11 illustrate a fastening device 56, a plurality of which may be used 'around the edge 57 of the pool to fasten down the margin of a cover 20. The edge 57 may be molded concrete or tile, for example. As shown, the fastener device 56 comprises essentially the cylindrical or tubular member 120 and the fastener member 122. The tubular member 120 is mounted in vertical position and embedded in the material defining the edge of the pool so that the top surface 124 of the tubular member is flush with the top horizontal surface 126. The tubular member 120 has an internal cylindrical surface portion 128 of uniform circular cross section throughout its length which is provided with-an enlarged or counterbored portion 130 at the upper end and an enlarged counterbored portion 132 at the lower end.

The fastener member 132 comprises an elongated cylindrical plunger 134 of uniform circular cross section throughout its length which is slightly smaller in diameter than the cylindrical portion 128 of the tubular member so as to be reciprocable and rotatable therein. The fastener member has an enlarged circular head 136 secured coaxially on the upper end of the plunger 134 which isfreely received in the counterbored portion whe'n'the fastener member 122 is retracted or lowered. This head has an inclined socket 138 adapted to receive a tool bypwhich the fastener member 122 may be rotated or raised and lowered. The fastener member 122 has an enlarged circular disc 140 secured coaxially on the lower end of plunger 134 which is freely slidable axially and rotatable in the lower counterbored portion 132 of the tubular member 120.

A pin 142 extends inwardly through the wall of the tubular member '120 having its inner end terminating in the counterbored portion 132 spaced a substantial distance above the bottom of the tubular member. The pin 142 extends inwardly far enough to underlie the disc 140 when the fastener member 122 is raised to the dotted-line position to hold the fastener member raised. However, the disc 140 has a clearance or relief 148 which clears the pin 142 in one rotative position of the fastener member 122 to allow the fastener member to be raised and lowered without interference from the A V-shaped mark 150 on the top of the head 136 of the fastener member is vertically aligned with the recess or clearance 148. This mark is adapted to be aligned with a similar mark 152 on the exposed upper endof the tubular member 120 to facilitate the alignment of the recess 148 with the pin 142. The mark 152 is vertically aligned with pin 142.

When the pool is covered, the fastener members 122 are raised to the dotted line position of use. This is accomplished by first rotating the fastener members 122 so that the marks 150 and 152 line up, thus vertically aligning the clearance 148 with pin 142. After the fastene'r member 122 is raised to the dotted line position, it is rotated to move the clearance 148 away from pin 142 so that the pin will support the fastener member in elevatedposition. Thenthe buttonholes 54 along the margins of the covers 20 may be pressed over the heads 136 of the fastener members 122 to secure the cover around the edge of the pool.

When it is desired to use the pool, the cover is unbuttoned from the fastening devices and the fastener members 122 are rotated to line up the clearances 148 with the pin 142 by aligning marks 150 and 152, allowing the fastener members 122 to descend by gravity to the solid line position. In the'solid line position, the flat top surfaces of heads 136 of fastener members 122 are flush with the top surface 126 of the edge surrounding the pool, thus allowing an unobstructed adjacent pool walking area.

I claim:

1. A swimming pool cover apparatus for covering a swimming pool when not in use, said apparatus comprising a pair of columns and a beam carried and supported by said-columns, said columns and said beam forming a bridge adapted to straddle the pool or to be located adjacent to one side of the pool,.said beam having a raised position and alowered position, said'beam being adapted to be positioned adjacent to the pool and movable between said lowered position near the top of the pool and said raised position spaced from the pool, power operated means associated with said columns for moving said beam vertically from one of said positions to the other, a pool cover of sufficient dimensions to cover a pool, and means for supporting said cover in an inoperative position in which the cover is wound up on said beam for storage and uncovers the swimming pool, said cover being extendible from said beam to overlie the pool in an operative position in which said cover covers the pool when said beam is in its lowered position said beam when in said raised position being elevated sufflciently to allow normal use of the pool.

2. The apparatus defined in claim 1, wherein means are provided for releasably securing the pool cover, when extended over the pool,-said releasable securing means comprising fastener elements having parts along the margin of said cover engageable with cooperable parts along the periphery of the pool.

3. The apparatus defined in claim 1, wherein said cover comprises a flexible sheet, and said supporting means comprises a roller upon which said sheet is adapted to be wound for storage.

4. The apparatus defined in claim 1, wherein said cover comprises a pair of flexible sheets, and said supporting means comprises rollers upon which said sheets are adapted respectively to be wound for storage.

5. The apparatus defined in claim 1, wherein said columns are in the form of fluid operated piston-cylinder assemblies to which said power operated means are attached for operating same.

6. The apparatus defined in claim 5, said power operated means further comprising a pump, a conduit from said pump to each piston-cylinder assembly to deliver fluid to the latter and elevate said beam to its raised position, check valve means in said conduit to retain the fluid in each piston-cylinder assembly and hold said beam in said raised position, and means for opening said check valve means to release the fluid in each piston-cylinder assembly and allow said beam to descend to its lowered position.

7. The apparatus defined in claim 1, wherein said columns are in the form of a pair of laterally spaced, upright fluid operated piston-cylinder assemblies respectively secured to and supporting the ends of said beam in substantially horizontal position, said beam and piston-cylinder assemblies constituting said bridge, and said power operated means operating said pistoncylinder assemblies.

8. The apparatus defined in claim 7, including guide means for guiding the up and down movement of said bridge.

9. The apparatus defined in claim 7, wherein said cover comprises a flexible sheet, said supporting means comprises a roller upon which said sheet is adapted to be wound for storage, and means for releasably securing the pool cover, when extended over the pool, said releasable securing means comprises fastener elements having parts along the margin of said sheet engageable with cooperable parts along the periphery of the pool.

10. The apparatus defined in claim 7, including vertical tubular guide means disposed in the ground, said piston-cylinder assemblies being anchored within said guide means and extending upwardly therefrom to said beam, and cooperating members on said pistoncylinder assemblies telescoping within said tubular guide means to guide the extension and contraction of said piston-cylinder assemblies.

1 l. The apparatus defined in claim 7, including vertical tubular guide means disposed entirely above ground, said piston-cylinder assemblies being anchored within said guide means and extending upwardly therefrom, and cooperating tubular members carried by said piston-cylinder assemblies and telescoping on said tubular guide means to guide the extension and retraction of said piston-cylinder assemblies, said beam being terminally secured to said cooperating tubular members.

12. The apparatus defined in claim 1, wherein means are provided for releasably securing the pool cover, when extended, over the pool, said releasable securing means comprises fastening devices each having a fastener member, and means mounting said fastener member adjacent the edge of the pool for vertical movement for a retracted position substantially flush with the surface area surrounding the pool to a raised position of use above said surface area.

13. The apparatus defined in claim 12, wherein said mounting means comprises an upright tubular member mounted in and with its top substantially flush with said surface area, and said fastener member is vertically movably mounted in said tubular member.

14. The apparatus defined in claim 13, wherein said fastener member and tubular member have cooperating means for holding said fastener member raised in one position of rotation thereof, said fastener member having means for clearing said cooperating means on said tubular member in another position of rotation of said fastener member to allow said fastener member to be retracted. 

1. A swimming pool cover apparatus for covering a swimming pool when not in use, said apparatus comprising a pair of columns and a beam carried and supported by said columns, said columns and said beam forming a bridge adapted to straddle the pool or to be located adjacent to one side of the pool, said beam having a raised position and a lowered position, said beam being adapted to be positioned adjacent to the pool and movable between said lowered position near the top of the pool and said raised position spaced from the pool, power operated means associated with said columns for moving said beam vertically from one of said positions to the other, a pool cover of sufficient dimensions to cover a pool, and means for supporting said cover in an inoperative position in which the cover is wound up on said beam for storage and uncovers the swimming pool, said cover being extendible from said beam to overlie the pool in an operative position in which said cover covers the pool when said beam is in its lowered position said beam when in said raised position being elevated sufficiently to allow normal use of the pool.
 2. The apparatus defined in claim 1, wherein means are provided for releasably securing the pool cover, when extended over the pool, said releasable securing means comprising fastener elements having parts along the margin of said cover engageable with cooperable parts along the periphery of the pool.
 3. The apparatus defined in claim 1, wherein said cover comprises a flexible sheet, and said supporting means comprises a roller upon which said sheet is adapted to be wound for storage.
 4. The apparatus defined in claim 1, wherein said cover comprises a pair of flexible sheets, and said supporting means comprises rollers upon which said sheets are adapted respectively to be wound for storage.
 5. The apparatus defined in claim 1, wherein said columns are in the form of fluid operated piston-cylinder assemblies to which said power operated means are attached for operating same.
 6. The apparatus defined in claim 5, said power operated means further comprising a pump, a conduit from said pump to each piston-cylinder assembly to deliver fluid to the latter and elevate said beam to its raised position, check valve means in said conduit to retain the fluid in each piston-cylinder assembly and hold said beam in said raised position, and means for opening said check valve means to release the fluid in each piston-cylinder assembly and allow said beam to descend to its lowered position.
 7. The apparatus defined in claim 1, wherein said columns are in the form of a pair of laterally spaced, upright fluid operated piston-cylindeR assemblies respectively secured to and supporting the ends of said beam in substantially horizontal position, said beam and piston-cylinder assemblies constituting said bridge, and said power operated means operating said piston-cylinder assemblies.
 8. The apparatus defined in claim 7, including guide means for guiding the up and down movement of said bridge.
 9. The apparatus defined in claim 7, wherein said cover comprises a flexible sheet, said supporting means comprises a roller upon which said sheet is adapted to be wound for storage, and means for releasably securing the pool cover, when extended over the pool, said releasable securing means comprises fastener elements having parts along the margin of said sheet engageable with cooperable parts along the periphery of the pool.
 10. The apparatus defined in claim 7, including vertical tubular guide means disposed in the ground, said piston-cylinder assemblies being anchored within said guide means and extending upwardly therefrom to said beam, and cooperating members on said piston-cylinder assemblies telescoping within said tubular guide means to guide the extension and contraction of said piston-cylinder assemblies.
 11. The apparatus defined in claim 7, including vertical tubular guide means disposed entirely above ground, said piston-cylinder assemblies being anchored within said guide means and extending upwardly therefrom, and cooperating tubular members carried by said piston-cylinder assemblies and telescoping on said tubular guide means to guide the extension and retraction of said piston-cylinder assemblies, said beam being terminally secured to said cooperating tubular members.
 12. The apparatus defined in claim 1, wherein means are provided for releasably securing the pool cover, when extended, over the pool, said releasable securing means comprises fastening devices each having a fastener member, and means mounting said fastener member adjacent the edge of the pool for vertical movement for a retracted position substantially flush with the surface area surrounding the pool to a raised position of use above said surface area.
 13. The apparatus defined in claim 12, wherein said mounting means comprises an upright tubular member mounted in and with its top substantially flush with said surface area, and said fastener member is vertically movably mounted in said tubular member.
 14. The apparatus defined in claim 13, wherein said fastener member and tubular member have cooperating means for holding said fastener member raised in one position of rotation thereof, said fastener member having means for clearing said cooperating means on said tubular member in another position of rotation of said fastener member to allow said fastener member to be retracted. 